An injection system of this type generally comprises a fuel injector and primary and secondary swirlers which are positioned downstream of the injector, coaxial therewith, and which each delimit a radial stream of air downstream of the injection of fuel so as to create the mixture of air and fuel that is to be injected into and then burnt in the combustion chamber. The airflows from the two swirlers are delimited by a Venturi interposed between the two swirlers and a bowl of frustoconical shape which is mounted downstream of the swirlers and which accelerate the flow of the air/fuel mixture towards the combustion chamber.
The Venturi has an interior surface with a narrowing or a constriction delimiting a premixing chamber in which some of the fuel ejected by the injector and the stream of air delivered by the primary swirler are mixed.
It has already been found that soot is deposited and coke is formed on this interior surface of the Venturi, and this leads to numerous disadvantages:                the deposits of soot and coke may form hot spots which shorten the life of the Venturi,        these deposits may also disrupt the airflow through the Venturi, the injection of fuel and the mixing of the fuel with the stream of air from the primary swirler, and        the presence of coke and of soot also increases the production of harmful gases which are discharged into the atmosphere.        